The telecommunications service vision for the future includes personal communications services (PCS), a term which denotes ubiquitous service for voice, data and other digital services from/to any place. The PCS service definition also includes radio ports for providing ubiquitous wireless access to the switched network from small, light-weight, low-power PCS radio terminals (portables or mobiles). Another future telecommunications network might be a wireless subscriber loop, in which the link between customers and the network is a fixed or nearly fixed radio link rather than copper twisted-pair. We illustrate our invention in the context of PCS but it is fully applicable to other radio access networks such as wireless subscriber loop.
With reference to FIG. 1A, an illustrative prior art proposed PCS network is shown. Each geographical area, called a microcell (M1-MM), includes a radio port (RP1-RPM) used to transmit and receive multiplexed radio frequency (RF) signals to/from multiple mobiles (101-110, 111-120). Each mobile has a separate channel in the multiplexed RF signal (e.g., 101 uses RF1). The different radio frequency (RF) channels served by a radio port are defined in time (i.e., TDMA), frequency (i.e., FDMA), or code space (i.e., CDMA), or some combination thereof. Each RF signal channel received by the radio port is processed by a multi-channel receiver module (e.g., MCR1) which produces a received digital signal stream from each channel (e.g., D1R from RF1R). Similarly, the transmitted signals require a multi-channel transmitter module (e.g., MCT1 ) at the radio port. The radio ports are connected via dedicated baseband digital lines (130) to a local radio access controller (140) which provides access to the switching network (160) via dedicated baseband digital lines (150).
In a PCS network, there are expected to be numerous radio ports, each using low power and radiating in a limited geographical area called a microcell. Smaller cells allow more frequency re-use within a geographical area, thus resulting in a larger capacity (maximum number of calls for given radio spectrum) in that area. With smaller cells, the RF transmission power can be lower. A microcell is expected to have a radius from 150 to 300 meters. For many scenarios, e.g., residential suburbs, the microcell size choice is driven more by low power (10 to 100 mW) requirements than capacity requirements. The small cell size results in a very large number of microcells, each with a radio port, needed to cover a given geographical area. Consequently, with the large number of radio ports needed, it is important that radio ports be low-cost. Also, a multitude of radio ports requires an extensive radio access controller and interconnection network for connecting all the radio ports. Thus, a continuing problem exists to reduce the cost of the physical implementation of a PCS network. In contrast to the cells of today's cellular systems, the average traffic demand per microcell is very small, with significant temporal variations. There exists a need for a system that can allocate capacity and resources to the microcells efficiently and dynamically in response to traffic fluctuations.
FIG. 1B shows another illustrative prior art proposed PCS network with analog RF transport and fixed simulcasting (for example, see Cablevision Systems Corporation's FCC Experimental License Progress Reports, November 1992 and August 1993). Radio access within a microcell (M1-MM) is provided by a platform microcell repeater (R1-RM). The multi-channel transmitter (MCT1) and receiver (MCR1) in FIGS. 1A and FIG. 1B are similar and operate in the same manner. In FIG. 1B, they are shared by the microcells M1-MM and located remotely from them in base station 180. The radio users in FIGS. 1A and FIG. 1B (101-110, 111-120) are identical and operate in the same manner. The air interface signals are transported in analog form between the repeaters R1-RM and the base station over coaxial cable network 170. In the repeaters, the downstream signals and upstream signals undergo block frequency conversion in the transmit block frequency converters (TFC1-TFCM) and the receive frequency converters (RFC1-RFCM), respectively. The base station 180 provides access to the switching network 160 using digital lines 150. Capacity is shared among a group of microcells by radiating the same air-frequency signal from the repeaters of the microcells in the group. In the upstream direction, the information received by each repeater is combined with that of other repeaters in the group. We call this mode of operation single-frequency simulcasting.
Prior art microcellular systems that use analog RF transport, like the one shown in FIG. 1B, use fixed simulcasting in which the composition of the simulcast group of microcells is predetermined and fixed. Since the microcells of a simulcast group also define a radio coverage area over which capacity is shared, there are fixed simulcast areas in which capacity is shared. The prior art includes the concept of cell-splitting in which a simulcast group is split into two simulcast groups in order to accommodate a growth in traffic. The prior art systems are limited, however, in that they cannot respond to dynamic variations in the spatial distribution of traffic. While the radio port in the prior art has some of the technology needed for effecting a reconfiguration of the simulcast group, tile prior art systems do not include a control architecture that supports dynamic reconfiguration. Moreover, superimposing a control architecture on the system shown in FIG. 1B is not sufficient.